Virtual Colon Screen Works for Seniors

Action Points

This study found that for most measures of diagnostic performance of virtual colonoscopy, including sensitivity and specificity, the difference between participants aged 65 or older and those younger than 65 years was not statistically significant.

Point out that the colonoscopy referral rate for detected adenomas was relatively small.

The diagnostic performance of virtual colonoscopy doesn't appear to be diminished in older patients, researchers found in a trial analysis that has reignited contention over the technology.

Sensitivity and specificity of CT colonography for large neoplasms both overall and on a per-polyp basis were statistically similar for a Medicare-age population and for those under 65, C. Daniel Johnson, MD, MMM, of the Mayo Clinic in Scottsdale, Ariz., and colleagues found.

The accuracy didn't differ for intermediate-sized lesions either, they reported in the May issue of Radiology.

"CT colonography can be used as a primary colorectal screening tool in patients older than 65 years, as well as in those age 50 to 65 years," Johnson's group concluded from the exploratory results.

The American College of Radiology and the partially industry-sponsored patient advocacy group Colon Cancer Alliance agreed, issuing a joint statement demanding coverage by Medicare.

CT colonography could boost screening rates and is already reimbursed by several major private insurers, they argued.

The Centers for Medicare and Medicaid declined to cover CT for colorectal cancer screening in 2009, siding with the U.S. Preventive Services Task Force in calling the evidence for virtual colonoscopy insufficient.

One of the agency's major points was that the technology wasn't proven for its population, because most trials included few Medicare-age patients or excluded them entirely.

Other issues cited were lower sensitivity than traditional colonoscopy for smaller lesions and higher cost since positive findings have to be confirmed and polyps removed in a separate procedure.

For this latest salvo in the ongoing battle over the evidence, Johnson's group conducted a post-hoc analysis of the American College of Radiology Imaging Network's National CT Colonography Trial.

Of the trial's 2,600 asymptomatic participants, 497 (19%) were 65 or older.

Not surprisingly, the prevalence of 1 cm or larger adenomas and colorectal cancers was higher in the older group at 7% versus 4% among those under 65. The referral rate for seniors was 13%.

There was no significant difference in diagnostic performance of CT colonography for most measures and most subsets.

For the primary endpoint of large, at least 10-mm histologically-confirmed colorectal neoplasia, results against optical colonoscopy as the reference standard were:

Sensitivity of 0.82 in the older cohort (95% CI 0.64 to 0.94) versus 0.92 in the younger group (95% CI 0.84 to 0.97)

Positive predictive value of 0.33 in the older group (95% CI 0.22 to 0.46) versus 0.20 in the younger group (95% CI 0.15 to 0.25)

Negative predictive value of 0.98 among seniors (95% CI 0.97 to 1.00) versus 1.00 among those under 65 (95% CI: 0.99 to 1.00)

For smaller diameter adenomas, the results were largely similar, with per-participant sensitivity for older versus younger participants that ranged from a low of 0.60 versus 0.67 with 5-mm adenomas up to 0.82 versus 0.91 for 9-mm adenomas.

Specificity for the smaller adenomas ranged from 0.83 to 0.86 for the older age group and from 0.86 to 0.89 for the younger group.

The only consistently significant performance difference between age groups was the higher negative predictive value for the younger group, but the difference decreased with larger polyp size and was unlikely to be clinically important, the researchers suggested.

But optimal bowel assessment was significantly less common in the older population, at just 10% compared with 36% in those under 65.

Optimal colon distention allowing good visualization was also less common after 65 with CT colonography (55% versus 66%).

"Awareness of this result could be managed by slower insufflation of the colon and vigilant review of the scout images before scanning," Johnson's group suggested. "Additional decubitus views might also be helpful."

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